The formation of perspiration is a normal and healthy bodily function. Perspiration, in itself, is odorless. However, the degradation of the protein compounds present in perspiration by natural, Gram-positive skin bacteria produces body odor, which in today's society is typically perceived as overpowering, repulsive and neglectful. For this reason, a large number of cosmetic products have been developed for bodycare with the aim of eliminating this unpleasant odor of perspiration. Application forms of such products, which include both odor-inhibiting deodorants and also perspiration-inhibiting antiperspirants, comprise sticks, creams, soaps, roll-ons, as well as aerosols and pump sprays.
There are various active principles which are useful in these standard commercial cosmetic formulations. For example, deodorants conceal the unpleasant odors through the addition of perfumes. Usually, deodorants also comprise antimicrobial active ingredients such as Triclosan®, ethereal oils or Farnesol®. Such materials act as bactericides or bacteriostats to reduce the natural bacterial flora on the skin, thus preventing the formation of odor. A further possibility is the use of antiperspirants, which reduce the perspiration secretion. The active ingredients used are aluminum and zirconium salts which, due to their protein-precipitating nature, narrow the sweat glands and thus reduce the formation of perspiration. Likewise prior art deodorant products also include enzyme blockers, such as triethyl citrate, which intervene in the enzymatic mechanism of bacterial decomposition of perspiration by preventing the formation of unpleasant-smelling degradation products by deactivating the ester-cleaving lipases.
Furthermore, so-called odor absorbers are also known. Odor absorbers are substances which can chemically or physically bond the odor-forming compounds by adsorption or absorption, respectively. One representative of such odor absorber material is zinc salts of ricinoleic acid, the preparation of which is described in DE-B-17 92 074.
The patent literature also includes descriptions in which these zinc salts are used in combinations with zinc salts of abietic acid or with zinc salts of other saturated or unsaturated hydroxylated fatty acids having 16 or more carbon atoms, and other active ingredients listed above.
Zinc ricinoleate can chemically bond odor-intensive organic substances with sulfur- or nitrogen-containing functional groups, such as, for example, mercaptans, thioethers, low molecular weight carboxylic acids, such as isovaleric acid, as well as amines. A particular advantage of this type of odor removal is that the bacterial equilibrium of the skin flora is not adversely affected as a result.
The ability of zinc ricinoleate to chemically firmly bond substances of this type permits zinc ricinoleate to be used in industrial areas of application for reducing unpleasant domestic and industrial odors.
However, due to its polymeric salt structure, zinc ricinoleate can only be used directly to a limited degree. Zinc ricinoleate is a compound which is only sparingly soluble in customary cosmetic solvents. In order to obtain effective preparations, zinc ricinoleate must be used in combination with solvents and solubility promoters. The typical solvents used are mono- or polyhydric alcohols, optionally with the addition of water. Customarily used highly ethoxylated solubility promoters are unable, even in high concentrations, to keep the zinc ricinoleate in solution by themselves and flowable products are also not obtained as a result.
Examples of special solubility promoters for zinc ricinoleate can be found in the patent literature. For example, patent specification DE-B-37 26 636 describes deodorants based on zinc ricinoleate with solvents and solubility promoters, where the solubility promoters used are the hydrolyzed ene adducts of ricinic fatty acids and maleic anhydride.
Patent specification DE-B-38 08 114 likewise describes deodorants based on zinc ricinoleate with solvent and solubility promoters. The solubility promoters used in this prior art reference are partial esters of di- or polyhydroxyalkanes, mono- and disaccharides, polyethylene glycols or alkanolamines with the ene adducts of maleic anhydride formed onto at least monounsaturated carboxylic acids with a chain length of from 10 to 25 carbon atoms and acid numbers from 10 to 140, which are preferably buffered to pH values around 6.5 with amino and/or amido compounds, such as triethanolamine, or glycol esters of aspartic acid and of glutamic acid as a result of the formation of salt-like bonds.
Preparations with these solubility promoters, however, were not flowable and the deodorant solutions formulated therefrom tend toward clouding and precipitation of individual components even at very low water contents (cf. DE-A-40 14 055 page 2, lines 50–52).
One improvement is the solution proposed in the patent specification DE-B-40 14 055, in which the applicants describe compositions with deodorizing action, comprising the zinc salt of ricinoleic acid and/or the zinc salt of abetic acid and/or further zinc salts of other saturated or unsaturated hydroxylated fatty acids having 16 or more carbon atoms, and also 5 to 50%, by weight, of an ethoxylated fatty alcohol with straight or branched alkyl chain and a carbon number between 10 and 18 with fewer than 30 ethylene oxide units per molecule, and 5 to 30%, by weight, of a tertiary amine.
The tertiary amines disclosed in the '055 reference are tertiary amino alcohols, such as, for example, triethanolamine or N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine.
The amino alcohols present in the prior art do not represent any problem for technical applications where there is no skin contact. For use in applications with skin contact, such as, in cosmetic products, however, more and more alternatives to amino alcohols are desired since the amino alcohols often comprise impurities of secondary amines. In addition, amino alcohols have also received negative headline coverage due to sensitizing and allergic reactions upon their use on skin.
Although the prior art formulations do represent very good progress, there is still a need for further improvement. For instance, the solubility in water or dilutability with water of the formulations without additional mono- and polyhydric alcohols as solubility promoters has still not been satisfactorily achieved.